The surgical technique of endoscopy allows a surgeon to perform diagnostic or surgical procedures in a minimally invasive manner. Laparoscopy requires inflating or insufflating the patient's abdominal cavity with gas. Distension of the abdomen by the insufflating gas allows the surgeon to visualize the organs and other internal structures by use of a laparoscopic telescope (laparoscope). The laparoscope is generally placed through an incision made in the umbilicus. Surgical instruments may be introduced either though a tureen in an operating laparoscope or through additional punctures in the abdominal wall.
The pressures necessary to adequately distend the abdomen are typically in the 12-14 mm Hg (0.25 psi) range. One of the concerns in this type of surgical procedure is the possibility of forcing some of the insufflating gas into an open blood vessel. Gas bubbles in the bloodstream may pose a risk of embolism. The use of various gases has been explored and the preferred gas for insufflating the patient is carbon dioxide (CO.sub.2). CO.sub.2 gas is preferred due to its rapid absorption in blood. This minimizes the potential for embolism.
One of the instruments commonly used through, or in conjunction with the laparoscope is the CO.sub.2 laser. This type of laser uses a CO.sub.2 molecule to generate an output wavelength of 10.6 .mu.. While this type of laser is very efficient in most applications for which it is intended, its efficacy ill endoscopy is adversely affected by the CO.sub.2 gas environment at the surgical site. Since the 10.6 micron wavelength of this laser is emitted by the CO.sub.2 molecule this molecule may also absorb photons of this wavelength. This phenomenon is called resonant absorption. When this occurs in the confines of the laparoscope lumen two things happen. First, the absorption of the 10.6 .mu. laser energy by the CO.sub.2 gas results in a loss of laser power transmitted to the target tissue. Second, the uneven heating of the CO.sub.2 gas in the laparoscope lumen results in creation of a gas lens within the lumen. This lensing causes distortion of the laser energy that does reach the tissue. This secondary gas lensing effect has an often dramatic effect in reducing the efficacy of the CO.sub.2 laser.
Another endoscopic procedure, arthroscopy, allows the surgeon to view or perform surgery on the internal structres of the joints through an arthroscopic telescope (arthroscope). Distension of the joint allows visualization of the internal structures. Though liquids are often used to distend the joint gas is used whenever a CO.sub.2 laser is to be employed. CO.sub.2 gas is generally preferred for this purpose. Again, the CO.sub.2 gas used to distend the joint can adversely affect the transmitted CO.sub.2 laser beam. One approach to this problem is to shift the output wavelength of the CO.sub.2 laser out of the absorption range of the CO.sub.2 insufflating gas. This wavelength shift is accomplished by changing the isotope of CO.sub.2 gas used in the laser gas mixture. See U.S. Pat. No. 5,062,842. One isotope used to generate the standard 10.6 .mu. wavelength is the C.sup.12 isotope. This is the most common isotope of CO.sub.2 gas and the same isotope that is used for insufflating the patient. For the 11.1 .mu. wavelength output, the less common C.sup.13 isotope of CO.sub.2 is used.
The possibility of using one of the other isotopes of CO.sub.2 gas as the insufflating medium was abandoned due to the extremely high cost of these gases. Due to the amount of CO.sub.2 gas consumed during the average procedure the cost per procedure would be prohibitive.
Another approach that has been taken is to increase the flow of CO.sub.2 gas through the lumen of the endoscope. As the rate of flow of the CO.sub.2 gas through the lumen is increased, the effect of the lensing is reduced. While the problem of loss of laser energy through absorption in the gas remains, the effects of the lensing are somewhat mitigated.
While research into the use of other gases for laparoscopic insufflation found that some institutions do use nitrous oxide (N.sub.2 O) gas, general resistance to this gas was high. In fact many anesthesiologists interviewed felt that use of any gas other than CO.sub.2 was too risky. While N.sub.2 O is more rapidly absorbed than many other gases, it is itself an anesthetic. Absorption of the gas within the cavity could unnecessarily complicate anesthesia during long procedures. N.sub.2 0 also supports combustion much as oxygen does. This can increase the likelihood of a fire should a heat source (laser) contact a flammable material in the operating theater.